Automotive fluids, such as engine oil or transmission fluids, absorb heat in use. To prevent fluid deterioration, this heat often needs to be removed. Heat exchangers are commonly used for this purpose. Moreover, heat exchangers are known to perform this function adequately in moderate ambient conditions. However, in cold ambient conditions, engine oils and transmission fluids can be highly viscous. In such conditions, these automotive fluids do not flow easily through heat exchangers. As a result, in such conditions, the fluid pressure within the lubrication circuit, and particularly within the heat exchangers, can be high enough to damage the heat exchangers. In some cases, starvation of some downstream components, like transmissions, may even occur.
In order to avoid these adverse effects, it is known to provide a mechanism for bypassing the heat exchanger. One way that this has been done in the past is to provide a bypass conduit. The bypass conduit is connected in parallel with the heat exchanger and has a relatively low resistance to the flow of high viscosity fluids as compared to the heat exchanger. Structures of this type are known to provide pressure relief for the heat exchanger and avoid starvation of the downstream components, but can suffer in that, in normal operating conditions, the flow is split between the heat exchanger and the bypass circuit. This requires that the heat exchangers be made proportionately larger and heavier to achieve the same overall heat exchange performance for the cooling system. This added size and weight, and the associated costs therewith, are undesirable to automotive manufacturers.
In U.S. Pat. No. 4,193,442 issued to David R. Vian, a heat exchanger is coupled to an adapter which is positioned between an oil filter and the engine. The adapter includes a valve in the form of a bimetallic strip that opens under normal operating conditions to allow flow through the heat exchanger, and closes in cold conditions to prevent flow through the heat exchanger. A difficulty with the Vian device, however, is that it is a rather large and bulky structure, and it still does not protect the heat exchanger from high fluid pressures in all conditions, especially if the oil filter is plugged or partially plugged.